Hypertension and diseases caused by hypertension are the leading cause of death in the world. Globally, one out of four adults, which correspond to about 100 million people, are said to suffer from these conditions. In particular, the risk of developing cardiovascular complications caused by hypertension is 2 to 4 times higher for diabetic patients than for non-diabetic patients. The International Diabetes Federation advocates the necessity of strict blood pressure control.
However, in spite of various treatments, blood pressure has not been reduced to the desired values in approximately 70% of hypertensive patients and in approximately 90% of patients suffering from both diabetes and hypertension. Although hypertension is recognized as a main risk factor for cardiovascular diseases such as cerebral apoplexy and myocardial infarction, it is not well known that insufficient blood pressure control (particularly, masked hypertension) is a more serious risk factor. In fact, it is reported that about 90% of hypertensive patients with cerebral infarction have been treated for hypertension before the onset of cerebral infarction. This precisely indicates that insufficient anti-hypertensive treatment causes cerebral apoplexy. The result of another clinical test reveals that the reduction of systolic blood pressure by only 10 mmHg can reduce the onset of cerebral apoplexy by about 40%. This result also indicates that “10 mmHg increase” in blood pressure is a very high risk factor.
Pharmaceuticals currently used for treating hypertension can be roughly classified into the following 6 types according to their mechanism of action:
(A) diuretics;
(B) calcium antagonists;
(C) angiotensin-receptor antagonists;
(D) angiotensin-converting enzyme inhibitors;
(E) beta blockers; and
(F) alpha blockers
Recently, anti-hypertensive peptides, which have an action of reducing blood pressure, have been attracting attention. Specific examples of anti-hypertensive peptides include biogenic peptides such as natriuretic peptides (ANP, BNP, CNP) (see, for example, Non-Patent Documents 1 to 3) and adrenomedullin (see Non-Patent Document 4); an enzymatic albumin hydrolysate Arg-Pro-Leu-X-Pro-Trp (wherein X is His, Lys, or Arg) (SEQ ID: NO. 7) (see Patent Document 1); and an enzymatic hydrolysate of soybean protein (see Non-Patent Document 5).
Presently, lifestyle habits are considered to have a strong influence on the onset of hypertension and dietary habits are continually being modified. Therefore, peptides derived from egg white or soybean, as described in Patent Document 1 or Non-Patent Document 5, are considered to be highly useful because these peptides are safe and can be produced by the ingestion and subsequent digestion of egg white or soybean.    Non-Patent Document 1: F. Yoshihara et al., Plasma atrial natriuretic peptide concentration inversely correlates with left atrial collagen volume fraction in patients with atrial fibrillation. Plasma ANP as a possible biochemical marker to predict the outcome of the maze procedure. J Am Coll Cardiol, 39, 288-294, 2002    Non-Patent Document 2: T. Norio et al., Gene expression and secretion, and autocrine action of C-type natriuretic peptide in cultured adult rat cardiac fibroblasts. Endocrinology, 144, 2279-2284, 2003    Non-Patent Document 3: Y. Takami et al., Diagnostic and prognostic value of plasma brain natriuretic peptide in non-dialysis-dependent chronic renal failure. Am J Kidney Dis, 44, 419-429, 2004    Non-Patent Document 4: F. Yoshihara et al., Possible involvement of oxidative stress in hypoxia-induced adrenomedullin secretion in cultured rat cardiomyocytes. Eur J Pharmacol, 436, 1-6, 2002    Non-Patent Document 5: Toshiro Matsui, “Production of Hypotensive Peptide, SVY, from 7S Globulin of Soybean Protein and Its Physiological Functions”, Soybean protein research, 6, 73-77, 2003    Patent Document 1: Japanese Unexamined Patent Publication No. 2002-80496